Sampling Techniques To Detect Hydrocarbon Seepage

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for detecting seepage of hydrocarbons in subterranean zones. In one aspect, a method includes detecting hydrocarbon seepage at multiple different sampling depths from a surface in a surveyed geographic region, comparing each of the hydrocarbon seepage at the multiple different sampling depths, wherein hydrocarbon seepage at a reference depth is known, and determining hydrocarbon seepage through the surveyed geographic region based on a result of the comparison.

TECHNICAL FIELD

This specification relates to detection of seepage of hydrocarbons fromsubterranean zones.

BACKGROUND

Hydrocarbons, such as oil and gas, can be geochemically detected fromparticular subterranean zones. The identification of subterranean zonesincluding hydrocarbon accumulations is becoming increasingly difficultto locate and access, as the demand for energy grows globally. In thepast, drilling was often performed near to a visible oil seep(macroseep) to access hydrocarbon accumulations. Presently, macroseepsare relatively rare and efforts directed towards identification ofhydrocarbon accumulations are mostly focused on detection of invisibleoil seeps (microseeps). Various geochemical methods can be utilized fornear surface exploration to measure data associated with microseeps. Forexample, sensitive instrumentation can be used for direct and indirectmicroseep detection methods. Improvements in technology and sensitivityof microseep detection methods may be beneficial in lowering the risk ofhydrocarbon exploration and efficiently locating subsurface hydrocarbonaccumulations.

SUMMARY

This specification describes geochemical methods relating to detectionof seepage of hydrocarbons from subterranean zones.

In some examples, a method of sampling a geographic region forhydrocarbon seepage includes detecting hydrocarbon seepage at a firstsampling depth from a surface in a surveyed geographic region, detectinghydrocarbon seepage at a second sampling depth from the surface, thesecond sampling depth deeper than the first sampling depth, detectinghydrocarbon seepage at a third sampling depth from the surface, thethird sampling depth deeper than the second sampling depth, comparingeach of the hydrocarbon seepage at the first sampling depth, thehydrocarbon seepage at the second sampling depth, and the hydrocarbonseepage at the third sampling depth with hydrocarbon seepage at areference depth deeper than the first, second and third sampling depths,wherein hydrocarbon seepage at the reference depth is known, anddetermining hydrocarbon seepage through the surveyed geographic regionbased on a result of comparing each of the hydrocarbon seepage at thefirst sampling depth, the hydrocarbon seepage at the second samplingdepth, and the hydrocarbon seepage at the third sampling depth with thehydrocarbon seepage at the reference depth.

In some implementations, detecting hydrocarbon seepage at the firstsampling depth includes, detecting hydrocarbon seepage at the secondsampling depth and detecting hydrocarbon seepage at the third samplingdepth includes: positioning a first plurality of hydrocarbon sensors atthe first sampling depth, positioning a second plurality of hydrocarbonsensors at the second sampling depth, and positioning a third pluralityof hydrocarbon sensors at the third sampling depth, wherein the firstplurality of hydrocarbon sensors, the second plurality of hydrocarbonsensors and the third plurality of hydrocarbon sensors are configured todetect hydrocarbons at the first sampling depth, the second samplingdepth and the third sampling depth, respectively.

In some implementations, detecting hydrocarbon seepage at the firstsampling depth includes, detecting hydrocarbon seepage at the secondsampling depth and detecting hydrocarbon seepage at the third samplingdepth includes: positioning a first plurality of hydrocarbon sensors atthe first sampling depth, positioning a second plurality of hydrocarbonsensors at the second sampling depth, and positioning a third pluralityof hydrocarbon sensors at the third sampling depth, wherein the firstplurality of hydrocarbon sensors, the second plurality of hydrocarbonsensors and the third plurality of hydrocarbon sensors are configured todetect hydrocarbons at the first sampling depth, the second samplingdepth and the third sampling depth, respectively.

In some implementations, positioning the first plurality of hydrocarbonsensors at the first sampling depth includes positioning the firstplurality of hydrocarbon sensors in a two-dimensional array at the firstsampling depth. The first sampling depth can be about 1.0 meter from thesurface.

In some implementations, positioning the second plurality of hydrocarbonsensors at the second sampling depth includes positioning the secondplurality of hydrocarbon sensors in a two-dimensional array at thesecond sampling depth. The second sampling depth can be about 5.0 meterfrom the surface.

In some implementations, positioning the third plurality of hydrocarbonsensors at the third sampling depth includes positioning the thirdplurality of hydrocarbon sensors in a two-dimensional array at the thirdsampling depth. The third sampling depth can be greater than 5.0 meterfrom the surface.

In some implementations, the method further includes positioning areference hydrocarbon sensor at the reference depth, the referencehydrocarbon sensor configured to detect hydrocarbons at the referencedepth. The reference depth can be within a hydrocarbon reservoir in thesurveyed geographic region.

In some implementations, comparing each of the hydrocarbon seepage atthe first sampling depth, the hydrocarbon seepage at the second samplingdepth, and the hydrocarbon seepage at the third sampling depth withhydrocarbon seepage at a reference depth deeper than the first, secondand third sampling depths includes detecting hydrocarbon seepage at thereference depth.

In some implementations, comparing each of the hydrocarbon seepage atthe first sampling depth, the hydrocarbon seepage at the second samplingdepth, and the hydrocarbon seepage at the third sampling depth withhydrocarbon seepage at a reference depth deeper than the first, secondand third sampling depths includes: determining a reference hydrocarbonseepage signal that represents the hydrocarbon seepage at the referencedepth, determining a first hydrocarbon seepage signal that representsthe hydrocarbon seepage at the first sampling depth, determining asecond hydrocarbon seepage signal that represents the hydrocarbonseepage at the second sampling depth, determining a third hydrocarbonseepage signal that represents the hydrocarbon seepage at the thirdsampling depth, subtracting the first hydrocarbon seepage signal fromthe reference hydrocarbon seepage signal, subtracting the secondhydrocarbon seepage signal from the reference hydrocarbon seepagesignal, and subtracting the third hydrocarbon seepage signal from thereference hydrocarbon seepage signal.

In some implementations, the hydrocarbon seepage at the first samplingdepth, the hydrocarbon seepage at the second sampling depth and thehydrocarbon seepage at the third sampling depth can be detected at afirst time instant and the method further includes: detecting, at asecond time instant after the first time instant, hydrocarbon seepage atthe first sampling depth, detecting, at the second time instant,hydrocarbon seepage at a second sampling depth from the surface, thesecond sampling depth deeper than the first sampling depth, detecting,at the second time instant, hydrocarbon seepage at a third samplingdepth from the surface, the third sampling depth deeper than the secondsampling depth, and comparing each of the hydrocarbon seepage at thefirst sampling depth detected at the second time instant, thehydrocarbon seepage at the second sampling depth detected at the secondtime instant, and the hydrocarbon seepage at the third sampling depthdetected at the second time instant with hydrocarbon seepage at thereference depth determined at the second time instant.

In some implementations, the method further includes determininghydrocarbon seepage through the surveyed geographic region as a functionof time based on a result of the comparing at the first time instant andthe comparing at the second time instant. The method can also furtherinclude analyzing, based on the hydrocarbon seepage the first samplingdepth, the hydrocarbon seepage at the second sampling depth, and thehydrocarbon seepage at the third sampling depth, a relationship betweenpolar compounds and non-polar compounds included in the hydrocarbon.

The present disclosure also provides another method that includesactions of in a surveyed geographic region, detecting hydrocarbonseepage at a plurality of depths from the surface, comparing thehydrocarbon seepage at the plurality of depths with known hydrocarbonseepage at a reference depth that is deeper than the plurality ofdepths, and determining hydrocarbon seepage through the surveyedgeographic region based on comparing the hydrocarbon seepage at theplurality of depths with known hydrocarbon seepage at the referencedepth.

In some implementations, detecting hydrocarbon seepage at the pluralityof depths from the surface includes positioning a plurality ofhydrocarbon sensors at each depth of the plurality of depths, eachhydrocarbon sensor configured to detect hydrocarbons at the respectivedepth. The plurality of depths includes three depths. The three depthsinclude depths about 1.0 meter from the surface, about 5.0 meter fromthe surface, and greater than 5.0 meter from the surface. At each depth,hydrocarbon seepage is detected at a plurality of locations.

In some implementations, detecting hydrocarbon seepage at a plurality oflocations includes positioning a plurality of hydrocarbon sensors in atwo-dimensional array at each depth. The reference depth is within thehydrocarbon reservoir.

In some implementations, the hydrocarbon seepage at the plurality ofdepths is detected at a first time instant, and the method furtherincludes: in the surveyed geographic region, detecting, at a second timeinstant after the first time instant, hydrocarbon seepage at theplurality of depths from the surface, comparing the hydrocarbon seepageat the plurality of depths at the second time instant with knownhydrocarbon seepage at the reference depth at the second time instant,and determining hydrocarbon seepage through the surveyed geographicregion as a function of time based on a result of the comparing at thefirst time instant and the comparing at the second time instant.

In some implementations, the method includes analyzing, based on thehydrocarbon seepage at the plurality of depths, a relationship betweenpolar compounds and non-polar compounds included in the hydrocarbon.

The present disclosure further provides another method that includesactions of inserting a plurality of gas sampling probes into asubterranean formation, such that each of the plurality of gas samplingprobes is inserted at a location different than the rest, detecting, ata first time instant, with each of the plurality of gas sampling probesa first set of geochemical data associated to the respective locations,determining a first spatial map based on the first set of geochemicaldata, detecting, at a second time instant, with each of the plurality ofgas sampling probes a second set of geochemical data associated to therespective locations, determining a second spatial map based on thesecond set of geochemical data, generating a spatio-temporal map basedon the first spatial map and the second spatial map, and determiningseepage of hydrocarbons based on processing the spatio-temporal map. Theplurality of gas sampling probes includes at least three gas samplingprobes. Each of the plurality of gas sampling probes includes arespective length different from the rest, such that each of theplurality of gas sampling probes is inserted at a respective depth inthe subterranean formation. At least one of the pluralities of gassampling probes includes a respective length that is larger than onemeter. The first and second set of geochemical data includes biologicaland chemical sampling of one or more of fluids, gases, and sediments.

In some implementations, determining the first and second spatial mapincludes measuring molecular and isotopic signatures of non-hydrocarbongases and hydrocarbons. In some implementations, processing thespatio-temporal map includes differentiating between active and passiveseepage. Processing the spatio-temporal map can also include filteringseepage signals.

In some implementations, determining seepage of hydrocarbons furtherincludes at least one of satellite, airborne, acoustic and seismictechniques. Determining seepage of hydrocarbons can also includedetermining depth, type, quality, volume and location of a subsurfacehydrocarbon.

The present disclosure further provides a system to detect hydrocarbons,the system includes: a plurality of gas sampling probes configured to beinserted into a subterranean formation, such that each of the pluralityof gas sampling probes is inserted at a location different than therest, a plurality of gas collection and concentrating devices, each ofthe plurality of gas collection and concentrating devices beingremovably attached to the plurality of gas sampling probes and beingconfigured to collect, at a first time instant, a first set ofgeochemical data associated to the respective locations and at a secondtime instant, a second set of geochemical data associated to therespective locations, and a processor configured to determine aspatio-temporal map based on the first set and the second of geochemicaldata and to determine seepage of hydrocarbons based on processing thespatio-temporal map. The system can further include a seismometerconfigured to detect seismic waves at the respective locations. Thedetails of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a multi-depth design for detectingseepage of hydrocarbons.

FIG. 2 is a flowchart of an example process for detecting seepage ofhydrocarbons.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

This specification relates to detection of hydrocarbon seepage and, inparticular, hydrocarbon microseepage. The hydrocarbon present insubterranean zones can include oil, water, gas and solid (for example,rock deposits). A direct method to detect hydrocarbon seepage caninclude measuring reservoir hydrocarbons through soil-gas surveys.Surface prospecting technology offers an inexpensive tool to validatethe presence of subsurface hydrocarbons ahead of the bit. Surfaceprospecting technology may reduce the overall exploration risk quitesubstantially if it can confirm the presence of hydrocarbons. Surfaceprospecting technology can also be used in prioritizing prospects and ininferring the nature of hydrocarbon accumulation (for example, oilversus gas). Surface prospecting technology can be used as an ancillaryand integral component of other exploration tools to enhance theirresolution.

Microseepage patterns are complex and can vary in space and over time.For example, in producing areas the gas concentration in overlyingsediments increases. Reservoirs that are over-pressured presumably leakmore intensely than under-pressured reservoirs. Active seepage leads tohigher concentrations of hydrocarbons to the surface that may be easilydetected by geochemical surveys. Fresh seepages may suggest an activegeneration and migration or, alternatively, leakage from an oldaccumulation induced by recent faulting/fracturing. Passive seepage canindicate a non-generating basin, resulting in weaker geochemicalexpressions at the surface, except in areas where major conduits arepresent such as faults. It is assumed that the geochemical expression atthe surface primarily reflect the type of accumulation (oil versus gas),although the original composition and primary signal can be altered byother geological factors such as seal type, depth of accumulation andstructural rejuvenation, among other factors. Knowledge of microseepageparameters including the concentration as a function of space and timecan improve exploration success and open new potential areas.

Particular specifications of the detection method described can beimplemented so as to realize one or more of the following advantages.The accuracy and reliability of the proposed method to detect themicroseepage parameters is independent of the amount of gas voidfraction. The multi-depth profiling method accounts for spatio-temporalvariability and non-stationary nature of the signal. Any of thedescribed method can be coupled with other subterranean explorationtools. The disclosed design engineered as a method to detect themicroseepage parameters can be performed at off-shore or on-shorelocations, such as in regions that were not previously explored for oildrilling or in regions including or near to old oil wells. The methodcharacteristics allow for an enhancement of the seepage signal bymeasuring at multiple depths in the same test location and could,therefore, reduce the noise or contaminant (from a single measurement)by identifying new seepage-sensitive parameters. The result of thismethod is independent of all other remote sensing methods such asseismic, potential field and land sat images. It can also be integratedwith other exploration methods such as seismic acquisition tosimultaneously measure both the seepage concentration as well as theseismic reflection time through geophones. Such integration is criticalin lowering the overall exploration risk.

As shown in FIG. 1, an example seepage detection system 100 can beimplemented before well production to identify microseepage patterns ina subterranean formation 102. Measurement of microseepage patterns canhelp locate prospects and, eventually, support the optimization of welldrilling and production. The example seep detection system 100 includesmultiple gas sampling probes 104, 106, and 108 at multiple depths. Thegas sampling probes 104, 106, and 108 can include a conventionalpost-run tubing gas sampling probe. In some implementations, the gassampling probes 104, 106, and 108 can be inserted into the subterraneanformation 102 by a “direct push” technique which involves the use of ahydraulically powered percussion machine to drive the tool into theground without having to remove soil and make a path for the tool. Insome implementations, a cordless rotary drill is used to drive the gassampling probes 104, 106, and 108 can be inserted into the subterraneanformation 102.

The gas sampling probes 104, 106, and 108 can include a tip 110, whichcan have a sharp end at the bottom and can be of a retractable or anexpendable type. Attached to the tip 110 can be a slotted hollow tube112 that has a plurality of vents or apertures through which gasesemanating from the adjacent soil 102 may enter the hollow interior ofthe tube. A gas-conducting adapter 114 interconnects the hollow tube 112with a rigid tubular driving shaft 116. The adapter 114 can includeopenings, such as vents and apertures, or the adapter 114 can be openedat the bottom to receive soil gases into the interior of the adapter. Insome cases, depending upon the type of the soil and the subterraneandepth selected to be studied, the hollow tube 112 can have differentlengths, being configured to enable the insertion of the gas samplingprobes 104, 106, and 108 at various depths.

The driving shaft 116 can be approximately the same length as theanticipated earth depth of the gas sampling probes 104, 106, and 108when it is fully inserted (for example, 1.0 meter, 5 meters or 110meters). The driving shaft 116 can conduct the hydraulic driving forceto position the probe below the surface of the soil being tested. Insome cases it is desirable to connect the tip 110 directly to theadapter 114. In such a case, after reaching the desired probe depth, thedriving shaft 116 can be retracted to separate the tip 110 from theadapter 114, creating a vertical tunnel in the soil between the probetip 110 and the vented bottom of the adapter 114, through which soilgases may flow to enter the adapter 114. In some implementations, thegas sampling probes 104, 106, and 108 include sorbers configured toabsorb gas molecules. The gas sampling probes 104, 106, and 108 can beinserted in the soil and left in the soil for preset time intervals (forexample, two weeks) that are sufficient to collect a significantquantity of soil gases that can be analyzed in the laboratory.

The soil gases that enter the interior of the adapter 114 can beconducted through the tubing 118 to a collecting and concentratingdevice 120, located at the surface. The collecting and concentratingdevice 120 can include a glass tube, or other suitable tubularmaterials. The collecting and concentrating device 120 can house aplurality of different granular materials packed in series within thetube, each of which acts as a molecular sieve for the different gaseswhich may be of interest in determining the characteristics of ahydrocarbon deposit possibly positioned below the location at which thegas sampling probes 104, 106, and 108 was inserted into the subterraneanformation 102. A molecular sieve is a material, whose surface pores areof such size as to admit the molecules of a certain gas which are thentrapped within the material until released through a thermal or chemicalprocess. By appropriate selection of the material, a particular gas maybe trapped. The collecting and concentrating device 120 and the packedfiltering materials therein can act to concentrate the lighthydrocarbons found in the soil gas sample.

The tubing 118 can also be connected to a control device 122 that canassist the collection of gasses. In some implementations, the controldevice 122 is a timer that monitors the period during which the gassampling probes 104, 106, and 108 are in the soil, collecting gas. Insome implementations, the control device 122 is a vacuum/volume type ofpump that is configured to actively draw the soil gases into the gassampling probes 104, 106, and 108 and upwardly through the tubing 118.The vacuum/volume pump can be shut off after sampling is complete andthe collecting and concentrating device 120 is disconnected from thetubing line 118 after the line pressure returns to ambient atmosphericpressure. The sample acquired by the gas sampling probes 104, 106, and108 or the collecting and concentrating device 120 can be processed, forexample at a lab to retrieve geochemical data. The geochemical data canbe transmitted to an acquisition and transmission system 124.

The acquisition and transmission system 124 can include multiple parts,such as a data acquisition and transmission system unit, to performfunctions, such as amplifying the signals if necessary, sampling anddigitizing the analogue signals into digit format by the dataacquisition unit, and transmission the digitized signals to the computer126. The acquisition and transmission system 124 can include a processorassembly, two encoder/decoder systems, and a conventional geochemicaltelemetry system. The acquisition and transmission system 124 caninclude components that are located within the gas sampling probes 104,106, and 108 and components that are located above the ground surface.The digitized geochemical signals, generated by the data acquisition andtransmission system 124, are sent to the computer 126. The computer 126can include various components such as, for example, an electronicprocessor 128, memory 130 contained within, carried by, or otherwiseoperably coupled with the electronic processor 128, and a hydrocarbonseepage analyzing program 132 stored therein, which can adapt thecomputer 126 to perform program functions. The digitized geochemicalsignals are read by the hydrocarbon seepage analyzing program memory 130or in a database 134 accessible to the processor 128 of the computer126. The hydrocarbon seepage analyzing program 132 analyzes thegeochemical signals to derive a three-dimensional spatial map or afour-dimensional spatio-temporal map of geochemical concentrationsmeasured at various locations over the survey area.

In some implementation, the acquisition and transmission system 124further receives data associated to the investigated subterranean zone102, from one or more other devices. For example, the acquisition andtransmission system 124 can receive seismic data from a seismometer,magnetic data from a magnetometer or gravity data from a gravimeterseismic data. In some implementation, the example seepage detectionsystem 100 can further include airborne and/or remote gas sensingtechniques.

FIG. 2 is a flow chart showing an example process 200 for detection ofhydrocarbon seepage. In some instances, the process 200 is used toassist the selection of a location for drilling. At 202, multiple (atleast 3) gas sampling probes are inserted into the subterraneanformation at different depths in different locations corresponding toparticularly selected points in a surveying area. For example, thepositions of the plurality of hydrocarbon sensors form a two-dimensionalarray at each depth. The depths, at which the gas sampling probes areinserted, can vary between 1.0 meters and 10 meters under the surfacelevel. The locations, at which the gas sampling probes are inserted, cancover a surface of several square kilometers (for example, 100 squarekilometers). The gas sampling probes can be inserted into thesubterranean formation at particular distances (for example, 1kilometer) apart from each other. The insertion location for the gassampling probes can be selected based on soil conditions and the desireddepth of the probe. The criterion for selecting the location of the gassampling probes is based on a gridded survey targeting an area that isgeologically prospective for hydrocarbon accumulations. The insertionlocations and depths of the gas sampling probes can be selected based ona grid that supports or matches a particular statistical method ofanalyzing the hydrocarbon seepage. The gas sampling probes (for example,sorbers) are horizontally and vertically spaced at a selected distancefrom each other within a selected space and the gas absorbed by each gassampling probe can be mapped out over the survey space. Results canidentify areas of high gas concentrations within the survey space,presumably corresponding to hydrocarbon accumulations in the subsurface.

In some implementations, the gas sampling probes can be attached to theleading end of a hollow steel driving shaft which is advanced into thesoil profile using a hydraulic hammer. The down-hole tools including theprobe tool, the driving shaft and the hydraulic hammer can beconventional pieces of equipment. One end of each polyethylene tube canbe attached to an adapter through a threaded fitting at preselecteddepths (for example, at 1.0 meter, at 5 meters and at depths larger than5 meters). A gas sampling probe can be inserted into the gas conductingtubing between the upper end of the driving shaft and the vacuum/volumepump. A sample volume (for example, a few nano-grams) can be passivelyabsorbed by the gas sampling probe during a particular time interval(for example, 14-17 days). The survey is considered completed at the endof the time interval. After the survey is completed, the gas samplingprobes are removed from the installation locations and the gas samplingprobes can be sent to a laboratory for analysis. The laboratory analysiscan include extraction and identification of multiple types ofhydrocarbons (C2-C20) adsorbed by each of the gas sensors. The resultsof the analysis can be stored in a database in association with thelocation of each gas sensor in the survey space. In someimplementations, methane (C1) is not measured due to the fact that itcan be generated from a biogenic source as well as a thermogenic source.The atmospheric gas can be removed from each gas sampling probe via avacuum/volume pump and it can be discarded to the atmosphere. In someimplementations, light hydrocarbons, such as ethane, propane, butane,pentane, hexane, other hydrocarbons and their isomers, helium and otherrare earth gases that may be present in the soil gas sample, can be“filtered” out of the soil gas or trapped in various packings that arecontained in the gas sampling probes (for example, concentrating device120 illustrated in FIG. 1). The gas probes can collect up to 100 gascompounds (including aromatic and non-aromatic hydrocarbons).

At 204, the samples collected in each gas sampling probes are analyzedto identify the presence and the concentration of gas compounds ofinterest relative to their corresponding location in the surveyedvolume. A portion of the collected gas compounds can be used todetermine the hydrocarbon seepage. In some implementations, the analysisof gas compounds includes the identification of hydrocarbons in therange C2-C20, their polar compounds and their relations to non-polarcompounds. The geochemical data associated with the location each gassampling probe can be combined based on the spatial coordinates forgenerating a three-dimensional spatial distribution of the geochemicalproperties in the investigated locations and depths. In someimplementations, the geochemical data are processed to reduce the noiseor contaminant by filtering particular seepage-sensitive parameters. Forexample, filtering is done geostatistically by collecting backgroundnoise collected at control points known to be barren from petroleumaccumulations or leaks, like dry holes. The geochemical data can includeseepage-induced magnetic anomalies associated with oil and gas fields,which can be integrated with other geologic information to select adrilling location for the well that takes into account the structuralcharacteristics (depth, width, and location) of the anomaly.

In some implementations, the seepage signature measured from a knownaccumulation having a defined geochemical signature can be compared toother seepage signatures measured at multiple selected depth intervalsto increase the accuracy of seepage identification. For example, over aknown hydrocarbon accumulation the composition of the gas is quantifiedand compared to that of the seepage obtained from multiple depths.Similar compounds can be attributed to the referenced accumulation andother compounds can be from non-targeted accumulations or noise. Theaccumulated compounds can be tested and verified over a known field. Thesignatures gathered from multiple depths versus a reference depth (forexample, a location with known hydrocarbon accumulation can becross-checked to subtract any noise or contaminant-related signals inorder to match the most resembled signature to the actual one). Theimpact of contaminants or noise at the surface decreases with depth.True gas seepage can be distinguished from false readings based on thevariation of hydrocarbon accumulation, which is approximately invariantor increases with depth. Performing a statistical analysis of the gascompounds, collected at multiple locations and depths, by combiningmulti-depth data can strengthen similarities (for example, increasesignificance of correlations) related to primary data and reduce noise.

At 206, the geochemical survey is repeated at different time intervals(for example, weeks or months apart) to investigate the hydrocarbonseepage variation over time and to generate a four-dimensional map ofhydrocarbon microseepage. The statistical analysis of the gas compoundsincluding the multi-depth comparison can be repeated at different timesto identify which compounds are consistently measured and which of themeasured compounds can be attributed to noise. The four-dimensional mapof hydrocarbon microseepage can include complex patterns that indicate asource (for example, geographical coordinates of a hydrocarbonreservoir) and a trend of the hydrocarbon seepage. At 208, the seepageof hydrocarbons is determined based on processing the four-dimensionalmap of hydrocarbon microseepage. In some implementations, thefour-dimensional map of hydrocarbon microseepage can indicate thespatio-temporal variation in seepage intensity in producing areas. At210, the variation in intensity can be used to identify the pressure ofidentified hydrocarbon reservoirs. For example, significantly increasingseepage intensity can indicate overpressured reservoirs and low seepageintensity can indicate underpressured reservoirs.

The four-dimensional map of hydrocarbon microseepage can indicate thevariation in concentrations of hydrocarbons in producing areas. Thevariation in concentrations of hydrocarbons can be used to identifyactive, passive, and fresh seepage. For example, active seepage leads tohigher concentrations of hydrocarbons to the surface that can bedetected based on the four-dimensional geochemical surveys. Freshseepages can be associated with an active generation and migrationsystem induced by faulting/fracturing and subsequent leakage from an oldaccumulation. Passive seepage can be detected based on thefour-dimensional geochemical surveys that indicate a non-generatingbasin, resulting in weaker geochemical expressions at the surface,except in areas where major conduits are present such as faults. In someimplementations, the geochemical expression at the surface can be usedto identify the type of accumulation (for example, oil versus gas).

In some implementations, the method for detection of hydrocarbon seepagecan utilize a combination of satellite, airborne, acoustic and seismictechniques along with underwater sensors to characterize and maphydrocarbons in a variety of environments. The combination ofgeophysical techniques along with multiple sensors provides a morecomplete characterization and mapping of hydrocarbons at basin scaleexploration areas. The various independent technologies may includeremote sensing (for example, satellite and/or airborne), seismic andacoustic imaging (for example, ship-based initially: multibeamechosounder, side-scan sonar, sub-bottom profiler; which may also beincluded in autonomous underwater vehicles (AUV) for unsurpassed imagingdue to proximity to seafloor, but much more local in scope), magneticand gravity surveying (either from ship or air-based tools, or from AUVmore locally), chemical sensing (AUV: primarily mass spectrometer andfluorometer), and sediment, biological and chemical sampling (forexample, piston cores typically, but may preferably utilize anunderwater vehicle to obtain sediment, fluid (oil, water), or and/or gassamples for noble gases and isotope logs, and biology). The method mayutilize airborne vehicles, ground vehicles, and marine vessels (forexample, ships and/or underwater vehicles (for example, unmannedunderwater vehicles, which may include remotely operated vehicles (ROVs)or AUVs). When combined into an integrated method, these technologiesmay determine the presence and location of thermogenic hydrocarbonseepages with complex patterns.

In some implementations, the method for detection of hydrocarbon seepagecan also include chemical sensing. The detection of thermogenichydrocarbons emanating from subterranean seeps, either at macro- ormicro-scale may be detected to confirm whether hydrocarbon seeps arepresent at identified locations. Measuring concentrations of thermogenicmethane, ethane, propane, butane, etc., near the seafloor can beperformed via compact high-sensitivity mass spectrometers and laserfluorometers (for aromatic compounds generally associated withhydrocarbon liquids). The seep vent location provides a favorable sitefor additional biological and chemical sampling of fluids, gases, andsediments to further enhance the analysis. In particular, this methodmay include determining the presence and estimating information, such asdepth, type, quality, volume and location, about a subsurfacehydrocarbon accumulation from the measured data from the underwatervehicle. In particular, the present techniques involve the use of threeindependent technologies: clumped isotope geochemistry, noble gasgeochemistry, and microbiology, which are combined and integrated as aworkflow to enhance hydrocarbon exploration success. The use of threeindependent technologies may provide information about the depth, fluidtype (oil versus gas) and quality, and volume of subsurface hydrocarbonaccumulations to be determined from the sampling and analysis of thefour-dimensional map of hydrocarbon microseepage combined with theancillary information. That is, the hydrocarbon seepage detection methodcan integrate a plurality of biological, geochemical, and seismicindicators, such as structural position and reservoir, seal, or trapconfiguration to enhance the accuracy of seepage identification. At 212,the seepage identification can be used to initiate drilling in ahydrocarbon reservoir.

Implementations of the subject matter and the operations described inthis specification can be implemented in digital electronic circuitry,or in computer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Implementations of the subjectmatter described in this specification can be implemented as one or morecomputer programs, i.e., one or more modules of computer programinstructions, encoded on computer storage medium for execution by, or tocontrol the operation of, data processing apparatus.

To provide for interaction with a user, implementations of the subjectmatter described in this specification can be implemented on any type ofcomputer having a display device, for displaying information to the userand a keyboard and a pointing device, for example, a mouse or atrackball, by which the user can provide input to the computer. Otherkinds of devices can be used to provide for interaction with a user aswell; for example, feedback provided to the user can be any form ofsensory feedback, for example, visual feedback, auditory feedback, ortactile feedback; and input from the user can be received in any form,including acoustic, speech, or tactile input.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what can be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features can be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination can be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingcan be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some cases, the actions recited in the claims can beperformed in a different order and still achieve desirable results. Inaddition, the processes depicted in the accompanying figures do notnecessarily require the particular order shown, or sequential order, toachieve desirable results. In certain implementations, multitasking andparallel processing can be advantageous.

What is claimed is: 1.-18. (canceled)
 19. A system to detecthydrocarbons, the system comprising: a plurality of gas sampling probesconfigured to be inserted into a subterranean formation, such that eachof the plurality of gas sampling probes is inserted at a locationdifferent than the rest; a plurality of gas collection and concentratingdevices, each of the plurality of gas collection and concentratingdevices being removably attached to the plurality of gas sampling probesand being configured to collect, at a first time instant, a first set ofgeochemical data associated to the respective locations and at a secondtime instant, a second set of geochemical data associated to therespective locations; and a processor configured to determine aspatio-temporal map based on the first set and the second of geochemicaldata and to determine seepage of hydrocarbons based on processing thespatio-temporal map.
 20. The system of claim 19, further comprising aseismometer configured to detect seismic waves at the respectivelocations.
 21. The system of claim 19, wherein the plurality of gassampling probes comprises a first gas sampling probe, a second gassampling probe and a third gas sampling probe, wherein the first gassampling probe is inserted at a first sampling depth from a surface inthe surveyed geographic region, the second gas sampling probe isinserted at a second sampling depth from the surface, the secondsampling depth deeper than the first sampling depth, and the third gassampling probe is inserted at a third sampling depth from the surface,the third sampling depth deeper than the second sampling depth.
 22. Thesystem of claim 21, wherein the first gas sampling probe comprises afirst plurality of hydrocarbon sensors positioned at the first samplingdepth.
 23. The system of claim 21, wherein the first plurality ofhydrocarbon sensors is arranged in a two-dimensional array at the firstsampling depth.
 24. The system of claim 21, wherein the first samplingdepth is about 1.0 meter from the surface.
 25. The system of claim 21,wherein the second gas sampling probe comprises a second plurality ofhydrocarbon sensors positioned at the second sampling depth.
 26. Thesystem of claim 25, wherein the second sampling depth is about 5.0meters from the surface.
 27. The system of claim 21, wherein the thirdgas sampling probe comprises a third plurality of hydrocarbon sensorspositioned at the third sampling depth.
 28. The system of claim 27,wherein the third sampling depth is about 10.0 meters from the surface.29. The method of claim 19, wherein the processor is configured toprocess the spatio-temporal map by differentiating between active andpassive seepage.
 30. The method of claim 19, wherein the processor isconfigured to process the spatio-temporal map by filteringseepage-sensitive parameters.
 31. The method of claim 30, wherein tofilter seepage-sensitive parameters, the processor is configured tocollect background noise at control points known to be barren fromhydrocarbon accumulation or leaks.